Battery charger cradle

ABSTRACT

In a battery charger cradle, a battery incorporated in a battery built-in device is charged by electric power induced to an induction coil. The cradle includes a primary coil for inducing electromotive force to the induction coil, a casing having a top plate atop of which the battery built-in device is placed, a movement mechanism for moving the primary coil along an inner surface of the top plate, and a position detection controller for detecting a position of the battery built-in device placed on the top plate and controlling the movement mechanism to bring the primary coil closer to the induction coil in the battery built-in device. When the battery built-in device is placed on the top plate, the position detection controller detects the position of the battery built-in device, and the movement mechanism moves the primary coil closer to the induction coil in the battery built-in device.

This is a continuation of Ser. No. 12/314,743, filed Dec. 16, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a battery charger cradle, on whichbattery built-in devices such as a battery pack and a mobile phone canbe placed, to recharge a built-in battery when electric power is carriedby the effect of electromagnetic induction.

2. Description of the Related Art

A battery charger cradle has been developed for recharging a built-inbattery, where electric power is carried from a primary coil to aninduction coil (a secondary coil) by the effect of electromagneticinduction. Refer to Japanese Patent Laid-Open Publication No. H09-63655(1997) and Japanese Utility Model Registration No. 3011829.

Described in Japanese Patent Laid-Open Publication No. H09-63655 (1997)is a structure in which the primary coil excited by an AC power sourceis incorporated in the battery charger cradle and the induction coilelectromagnetically coupled to the primary coil is incorporated in abattery pack. The battery pack also incorporates a circuit in which analternating current induced to the induction coil is rectified andsupplied to the rechargeable battery for a charging operation. Inaccordance with such structure, the battery pack is placed on thebattery charger cradle so that the battery contained in the battery packcan be recharged in a non-contact state.

Japanese Utility Model Registration No. 3011829 describes a structure inwhich the battery is contained in the bottom of the battery built-indevice and a secondary-side charging adaptor is provided subjacently tothe battery so that the induction coil and charging circuit areincorporated in the secondary-side charging adaptor. Also described is astructure in which the primary coil electromagnetically coupled to theinduction coil is provided in the battery charger cradle. The batterybuilt-in device coupled to the secondary-side charging adaptor is placedon the battery charger cradle, and the electric power is carried fromthe primary coil to the induction coil to recharge the battery containedin the battery built-in device.

SUMMARY OF THE INVENTION

Japanese Patent Laid-Open Publication No. H09-63655 (1997) presents adrawback that, when the battery pack on the battery charger cradle isout of alignment, the battery pack cannot be charged. This is because,when a relative position between the mobile electronic device and thebattery charger cradle is out of alignment, the primary coil and theinduction coil are not electromagnetically coupled to each other, andsuch state disables AC electric power to be carried from the primarycoil to the induction coil. Such drawback can be remedied, as describedin Japanese Utility Model Registration No. 3011829, when a positioningprotrusion is provided on the battery charger cradle and also apositioning recess is provided in the mobile electronic device, with thepositioning protrusion being fitted in the positioning recess. In suchstructure, the positioning protrusion is guided into the positioningrecess, enabling a relative misalignment to be avoided between themobile electronic device and the battery charger cradle.

The structure disclosed in Japanese Utility Model Registration No.3011829, however, presents a drawback in that it is time-consuming andcumbersome to set the battery built-in device in place because thebattery built-in device is placed on the battery charger cradle suchthat the positioning protrusion is guided into the positioning recess.Another drawback presented in this structure is that it is difficult forall users to always set the battery built-in device on the batterycharger cradle in a normal manner. Even another drawback presented insuch structure is that the battery built-in device cannot be made thinenough because the positioning recess is provided in the casing bottomand the induction coil is disposed superjacent to the positioningrecess. Since a battery built-in device such as a mobile phone isrequired to be made as thin as possible, an increased thickness causedby the positioning recess presents a drawback that convenientportability is spoiled.

The above-mentioned drawbacks can be overcome when a magnetic field forcarrying the electric power to the induction coil is generated over alarge area of the entire top surface of the battery charger cradle. Thisstructure, however, also presents a drawback in that efficiencydecreases in the electricity to be carried from the primary coil to theinduction coil because the magnetic field is also generated in portionswhere the battery built-in device is not placed. The structure alsosuffers the disadvantage that, when a metallic element such as iron isplaced atop of the battery built-in device, heat is likely to begenerated when an electric current flows to the metallic element by theeffect of electromagnetic induction.

The present invention has been made to overcome the above-mentioneddrawbacks. It is the primary object to provide a battery charger cradleon which a built-in battery can be efficiently recharged wherever abattery built-in device is placed atop of the casing.

Further, another important object of the present invention is to providea battery charger cradle in which the electric power can be efficientlycarried from the primary coil to the induction coil, assuring safety inuse because, even when another metallic element is placed atop of thecasing together with the battery built-in device, heat is not generatedby an electric current flowing to the metallic element by the effect ofelectromagnetic induction.

In order to achieve the above-described objects, the battery chargercradle of the present invention is provided with the followingcomposition.

The battery charger cradle is designed to be used with a batterybuilt-in device 50, 90 incorporating an electromagnetically coupledinduction coil 51 and also incorporating a battery that is recharged byelectric power induced to the induction coil 51. The battery chargercradle includes a primary coil 11 connected to an AC power source 12, 82for inducing electromotive force to the induction coil 51, a casing 20containing the primary coil 11 and having a top plate 21 on the top ofwhich the battery built-in device 50, 90 is to be placed, a movementmechanism 13 contained in the casing 20 for moving the primary coil 11along the inner surface of the top plate 21, and a position detectioncontroller 14, 64 detecting a position of the battery built-in device50, 90 placed on the top plate 21 and controlling the movement mechanism13 to bring the primary coil 11 closer to the induction coil 51contained in the battery built-in device 50, 90. In the battery chargercradle, when the battery built-in device 50, 90 is placed on the topplate 21 of the casing 20, the position detection controller 14, 64detects the position of the battery built-in device 50, 90, the positiondetection controller 14, 64 controls the movement mechanism 13, and themovement mechanism 13 moves the primary coil 11 along the top plate 21to bring the primary coil 11 closer to the induction coil 51 containedin the battery built-in device 50, 90.

The above described battery charger cradle carries the advantage thatthe built-in battery can be efficiently charged wherever the batterybuilt-in device is placed on the top surface of the casing. This isbecause, while the above described battery charger cradle incorporates,in the casing having the top plate, the primary coil for inducingelectromotive force to the induction coil contained in the batterybuilt-in device, the battery charger cradle is provided with themovement mechanism for moving the primary coil along the inner surfaceof the top plate and is also provided with the position detectioncontroller detecting the position of the battery built-in device to beplaced on the top plate and controlling the movement mechanism to bringthe primary coil closer to the induction coil contained in the batterybuilt-in device; and further, when the battery built-in device is placedon the top plate of the casing, the position of the battery built-indevice is detected by the position detection controller, and theposition detection controller controls the movement mechanism to bringthe primary coil closer to the induction coil contained in the batterybuilt-in device. In the battery charger cradle of this structure, sincethe position detection controller detects the position of the batterybuilt-in device to be placed on the top surface of the casing andcontrols the movement mechanism to bring the primary coil closer to theinduction coil contained in the battery built-in device, and so whereverthe battery built-in device is placed on the top surface of the casing,the battery incorporated in the battery built-in device can beefficiently charged when the primary coil is brought closer to theinduction coil and the electric power is efficiently carried from theprimary coil to the induction coil.

Particularly, in the above-described battery charger cradle, thebuilt-in battery can be efficiently charged by very easily placing thebattery built-in device on the battery charger cradle, unlike in aconventional case where the battery built-in device has to be placed ata prescribed spot of the battery charger cradle, for example, by guidingthe positioning protrusion to be fitted into the positioning recess,that is, by determining a position for connection. As can be seen fromthe above description, the battery charger cradle where such positioningprotrusion, positioning recess and the like are not required alsocarries the advantage that the battery built-in device can be designedto be thin enough for convenient mobility.

Further, the above-described battery charger cradle carries theadvantage that, because the position detection controller detects theposition of the battery built-in device placed on the top plate of thecasing and the primary coil is brought closer to the induction coil tocharge the battery contained in the battery built-in device, even whenother metallic element is placed together with the battery built-indevice on the top surface of the casing, safe use of the battery chargercradle can be assured by securely inhibiting a current flow which mightbe caused by (the effect of) the electromagnetic induction to suchmetallic element.

Further, the above-described battery charger cradle carries theadvantage that the top plate of the casing is so sized as to allow aplurality of battery built-in devices to be placed on, and when the fullcharge detection circuit in the position detection controller detects afull charge state of a battery contained in the battery built-in devicebeing subjected to a charging operation, a position of a non-chargedbattery built-in device incorporating a battery which is not fullycharged is detected, the movement mechanism is controlled to bring theprimary coil closer to the induction coil contained in the batterybuilt-in device to charge the battery contained in the non-chargedbattery built-in device, and thus when the plurality of battery built-indevices are placed on the top plate, the batteries contained in thebattery built-in devices can be switched one after another to be fullycharged.

Further, in the above-described battery charger cradle, since theposition detection controller detects the position of the induction coiland brings the primary coil closer to the induction coil, an efficientcharging operation can be effected by bringing the primary coilprecisely closer to the induction coil. Particularly, in this batterycharger cradle, since the position of the induction coil contained inthe battery built-in device is detected by the position detectioncontroller and the primary coil is brought closer to the induction coil,the built-in battery can be efficiently charged by detecting theposition of the induction coil contained in the battery built-in deviceby means of the position detecting controller in a state of placingvarious battery built-in devices on the top plate of the battery chargercradle, regardless of a structure or model of the battery built-indevice, in other words, regardless of the position of the induction coilcontained in the battery built-in device.

Further, in the above-described battery charger cradle, since theposition detection controller moves the primary coil along the top platein the directions of X axis and Y axis to be brought closer to theinduction coil, the primary coil can be quickly brought closer to theinduction coil, with a simplified structure of the movement mechanism.

Further, in the structure of the above-described battery charger cradle,since the position detection controller includes a plurality of positiondetection coils fixed to the top plate, a pulsed power source forsupplying a pulse signal to the position detection coil, a receivercircuit 32 for receiving an echo signal outputted to the positiondetection coil from the induction coil which is excited by the pulsesignal supplied from the pulsed power source to the position detectioncoil, and a discrimination decision circuit for judging a position ofthe induction coil on the basis of the echo signal received by thereceiver circuit, a precise position of the induction coil can beelectrically checked on the basis of the echo signal outputted from theinduction coil, namely, by an electrical signal.

Further, the structure of the above-described battery charger cradlecarries the advantage that, since the AC power source has a self-excitedoscillation circuit, and the position detection controller detects theposition of the induction coil on the basis of an oscillating frequencyof the self-excited oscillation circuit to control the movementmechanism, a position of the induction coil can be precisely detected.

Further, the structure of the above-described battery charger cradlecarries the advantage that, since the position detection controller iscomposed of a first position detection controller for roughly detectinga position of the induction coil contained in the battery built-indevice and a second position detection controller for preciselydetecting the position of the induction coil, the primary coil havingbeen brought closer to the induction coil by the first positiondetection controller is then brought even closer to the induction coilby the second position detection controller, and thus the induction coilcan be positioned more precisely.

Particularly, in the structure of the above-described battery chargercradle, since the first position detection controller transmits thepulse signal to the plurality of position detection coils fixed to thetop plate and the receiver circuit receives the echo signal outputted tothe position detection coil from the induction coil which is excited bythe pulse signal to judge the position of the induction coil, theposition of the induction coil can be electrically checked by means ofthe plurality of position detection coils over a wide area fordetection. This structure, enabling a wide area to be efficientlydetected, is very effective as the first position detection controllerfor roughly detecting the position of the induction coil contained inthe battery built-in device.

Furthermore, in the above-described battery charger cradle, since thesecond position detection controller precisely detects the position ofthe induction coil on the basis of the oscillating frequency of theself-excited oscillation circuit possessed by the AC power source, thestructure is effective enough as the second position detectioncontroller for precisely detecting the position of the induction coil.

Further, in the above-described battery charger cradle, the positiondetection controller includes a plurality of position detection coilsfixed to the top plate, a pulsed power source for supplying a pulsesignal to the position detection coil(s), a receiver circuit forreceiving the echo signal outputted to the position detection coil fromthe induction coil which is excited by the pulse signal supplied fromthe pulsed power source to the position detection coil, and adiscrimination decision circuit for judging a position of the primarycoil on the basis of the echo signal received by the receiver circuit;since the discrimination decision circuit detects the position of theinduction coil by comparing the level of the echo signal induced to eachof the position detection coils with the level of the echo signal storedin the memory circuit in the discrimination decision circuit, theposition of the induction coil can be precisely detected on the basis ofthe level of echo signal induced to the position detection coil. In thisbattery charger cradle, when the position of the induction coil isprecisely detected by the position detection controller, the built-inbattery can be efficiently charged by quickly bringing the primary coilcloser to the induction coil.

In the above-described battery charger cradle, the second positiondetection controller 14C can be arranged to move the primary coil 11 andstop the primary coil 11 at a position where a voltage of the primarycoil 11 becomes the lowest. Further, in the above-described batterycharger cradle, the second position detection controller 14C can also bearranged to move the primary coil 11 and stop the primary coil 11 at aposition where power consumption of an AC power source 82 becomes thesmallest. Furthermore, in the above-described battery charger cradle,the second position detection controller 14C can also be arranged tomove the primary coil 11 and stop the primary coil 11 at a positionwhere an electric current flowing through the induction coil 51 becomesthe largest.

The above and further objects of the present invention as well as thefeatures thereof will become more apparent from the following detaileddescription to be made in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of the battery charger cradle inaccordance with an embodiment of the present invention;

FIG. 2 is a block schematic diagram of the battery charger cradle inaccordance with an embodiment of the present invention;

FIG. 3 is a vertical cross-sectional view, as viewed orthogonally to Xaxis, of the battery charger cradle shown in FIG. 2;

FIG. 4 is a vertical cross-sectional view, as viewed orthogonally to Yaxis, of the battery charger cradle shown in FIG. 2;

FIG. 5 is a circuit diagram showing the position detection controllercontained in the battery charger cradle in accordance with an embodimentof the present invention;

FIG. 6 is a block diagram showing the battery charger cradle and thebattery built-in device in accordance with an embodiment of the presentinvention;

FIG. 7 is a graph showing an exemplary echo signal outputted from theinduction coil being excited by the pulse signal;

FIG. 8 is a graph showing a variation in the oscillating frequency withrespect to the relative displacement between the primary coil and theinduction coil;

FIG. 9 is a circuit diagram showing the position detection circuitcontained in the battery charger cradle in accordance with anotherembodiment of the present invention;

FIG. 10 is a graph showing the level of the echo signal induced to theposition detection coil in the position detection controller shown inFIG. 9;

FIG. 11 is a circuit diagram showing the position detection controllercontained in the battery charger cradle in accordance with analternative embodiment of the present invention;

FIG. 12 is a graph showing the variation in the voltage at the primarycoil with respect to the relative displacement between the primary coiland the induction coil;

FIG. 13 is a graph showing the variation in the power consumption at theAC power source supplying the electric power to the primary coil withrespect to the relative displacement between the primary coil and theinduction coil; and

FIG. 14 is a graph showing the variation in the electric current flowingthrough the induction coil with respect to the relative displacementbetween the primary coil and the induction coil.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

FIG. 1 through FIG. 6 show block schematic diagrams and principlediagrams of a battery charger cradle. As shown in FIG. 1 and FIG. 6, thebattery charger cradle 10 is so designed as to place a battery built-indevice 50 atop of the battery charger cradle 10 and charge a built-inbattery 52 contained in a battery built-in device 50 by the effect ofelectromagnetic induction. The battery built-in device 50 incorporatesan induction coil 51 electromagnetically coupled to a primary coil 11.The battery built-in device 50 contains a battery 52 that is charged byelectric power induced to the induction coil 51. Instead, the batterybuilt-in device 50 may be a battery pack.

FIG. 6 shows a circuit diagram of the battery built-in device 50. Thebattery built-in device 50 has a capacitor 53 being parallel-connectedto the induction coil 51. The capacitor 53 and the induction coil 51constitute a parallel resonance circuit 54. A resonance frequency of thecapacitor 53 and the induction coil 51, as a frequency similar to afrequency electrically carried from the primary coil 11, can beelectrically carried from the primary coil 11 to the induction coil 51in an efficient manner. The battery built-in device 50 shown in FIG. 6includes a rectifier circuit 57 composed of a diode 55 for rectifying analternating current outputted from the induction coil 51 and a smoothingcapacitor 56 for smoothing a pulsating flow having been rectified, and acharge control circuit 58 for charging a battery 52 by using a directcurrent outputted from the rectifier circuit 57. The charge controlcircuit 58 stops a charging operation when detecting a full charge stateof the battery 52.

As shown in FIG. 1 through FIG. 6, the battery charger cradle 10includes a primary coil 11 connected to an AC power source 12 forinducing electromotive force to the induction coil 51, a casing 20containing the primary coil 11 and having a top plate 21 on the top ofwhich the battery built-in device 50 is placed, a movement mechanism 13contained inside the casing 20 for moving the primary coil 11 along theinner surface of the top plate 21, and a position detection controller14 for detecting a position of the battery built-in device 50 placed onthe top plate 21 and controlling the movement mechanism 13 to bring theprimary coil 11 closer to the induction coil 51 contained in the batterybuilt-in device 50. The battery charger cradle 10 contains, in thecasing 20, the AC power source 12, the movement mechanism 13 and theposition detection controller 14.

The battery charger cradle 10 is so designed as to charge the built-inbattery 52 contained in the battery built-in device 50 in the followingoperations.

(1) When the battery built-in device 50 is placed on the top plate 21 ofthe casing 20, a position of the battery built-in device 50 is detectedby the position detection controller 14.

(2) The position detection controller 14 having detected the position ofthe battery built-in device 50 controls the movement mechanism 13, movesthe primary coil 11 along the top plate 21 by means of the movementmechanism 13, and brings the primary coil 11 closer to the inductioncoil 51 contained in the battery built-in device 50.

(3) The primary coil 11 brought closer to the induction coil 51 iselectromagnetically coupled to the induction coil 51 to carry AC powerto the induction coil 51.

(4) The battery built-in device 50 rectifies the AC power at theinduction coil 51 to be converted into a direct current, and thus thebuilt-in battery 52 is charged by the direct current.

The battery charger cradle 10 charging the battery 52 contained in thebattery built-in device 50 in accordance with the above-describedoperations contains inside the casing 20 the primary coil 11 connectedto the AC power source 12. The primary coil 11, being disposed beneaththe top plate 21 of the casing 20, is arranged so as to move along thetop plate 21. Efficiency of carrying the electric power from the primarycoil 11 to the induction coil 51 can be improved by narrowing a distancebetween the primary coil 11 and the induction coil 51. Preferably, in astate of bringing the primary coil 11 closer to the induction coil 51,the distance between the primary coil 11 and the induction coil 51 isset to be smaller than or equal to 7 mm. Thus, the primary coil 11,being beneath the top plate 21, is disposed as close to the top plate 21as possible. Since the primary coil 11 moves so as to be brought closerto the induction coil 51 contained in the battery built-in device 50placed on the top plate 21, the primary coil 11 is arranged so as to bemoveable along the lower surface of the top plate 21.

The casing 20 containing the primary coil 11 is provided with the planartop plate 21 on the top of which the battery built-in device 50 isplaced. In regard to the illustrated battery charger cradle 10, the topplate 21 being planar in its entirety is disposed horizontally. The topplate 21 is so sized as to allow a variety of battery built-in devices50 with different sizes and contours to be placed thereon, for example,the top plate 21 being of a square shape with one side being 5-30 cm orof a circular shape with a diameter of 5-30 cm. In the battery chargercradle of the present invention, the top plate may also be made larger,namely large enough to allow a plurality of battery built-in devices tobe simultaneously placed on, in order that the built-in batteriescontained in the plurality of battery built-in devices thussimultaneously placed may be charged one after another. Further, the topplate may be provided with peripheral walls or the like in thecircumference, and the battery built-in device may be placed inside theperipheral walls to charge the built-in battery.

The primary coil 11 is spirally wound on a plane parallel to the topplate 21 and emits an AC magnetic flux toward the top plate 21. Theprimary coil 11 emits the AC magnetic flux being orthogonal to the topplate 21 toward the top plate 21. When the AC power is supplied from theAC power source 12, the primary coil 11 emits the AC magnetic fluxtoward the top plate 21. The primary coil 11 can be arranged so as tohave larger inductance by winding a wire rod on a core 15 made of amagnetic material. The core 15, made of a magnetic material such asferrite having larger magnetic permeability, is of a barrel shape withits top being open. The barrel-shaped core 15 is of a shape in which acolumnar portion 15A disposed in the center of the spirally woundprimary coil 11 is connected, at the bottom portion, to the tubularportion 15B disposed externally. The primary coil 11 with the core 15can focus the magnetic flux to a specific portion to efficiently carrythe electric power to the induction coil 51. However, the primary coildoes not necessarily have to be provided with such core, and may be anair-core coil, instead. Since the air-core coil is lighter in weight,the movement mechanism for moving the air-core coil along the innersurface of the top plate can be simplified (in structure). The primarycoil 11, with its diameter being made generally equal to the outerdiameter of the induction coil 51, carries the electric powerefficiently to the induction coil 51.

The AC power source 12 supplies high-frequency power ranging, forexample, from 20 kHz to 1 MHz to the primary coil 11. The AC powersource 12 is connected via a flexible lead wire 16 to the primary coil11. This is because the primary coil 11 is moved in order to be broughtcloser to the induction coil 51 contained in the battery built-in device50 placed on the top plate 21. Although not shown, the AC power source12 includes a self-excited oscillation circuit and a power amplifier forelectrically amplifying the alternating current outputted from theoscillation circuit. In the self-excited oscillation circuit, theprimary coil 11 is used as an oscillation coil. Therefore, in thisoscillation circuit, an oscillating frequency is varied in accordancewith the inductance of the primary coil 11. The inductance at theprimary coil 11 is varied in accordance with a relative position betweenthe primary coil 11 and the induction coil 51. This is because mutualinductance with respect to the primary coil 11 and the induction coil 51is varied in accordance with the relative position between the primarycoil 11 and the induction coil 51. Therefore, the self-excitedoscillation circuit using the primary coil 11 as the oscillation coil isvaried as the AC power source 12 is brought closer to the induction coil51. For such reason, the self-excited oscillation circuit can detect therelative position between the primary coil 11 and the induction coil 51in accordance with the variation in the oscillating frequency, and theoscillation circuit can be used as the position detection controller 14as well.

The primary coil 11 is moved by the movement mechanism 13 to be broughtcloser to the induction coil 51. The movement mechanism 13 shown in FIG.1 through FIG. 4 moves the primary coil 11 along the top plate 21 in thedirections of the X axis and the Y axis to bring the primary coil 11closer to the induction coil 51. In the illustrated movement mechanism13, the primary coil 11 is brought closer to the induction coil 51 byrotating a threaded rod 23 by using a servomotor 22 and by moving a nutelement 24 screwed on the threaded rod 23. The servomotor 22 includes anX-axis servomotor 22A for moving the primary coil 11 in the direction ofthe X axis and a Y-axis servomotor 22B for moving the primary coil 11 inthe direction of the Y axis. The threaded rod 23 includes a pair ofX-axial threaded rods 23A for moving the primary coil 11 in thedirection of the X axis and a Y-axial threaded rod 23B for moving theprimary coil 11 in the direction of the Y axis. The pair of X-axialthreaded rods 23A are disposed in a mutually parallel relationship,driven by means of a belt 25, and rotated together by means of theX-axis servomotor 22A. The nut element 24 includes a pair of X-axis nutelements 24A threaded on each of the X-axial threaded rods 23A and aY-axis nut element 24B threaded on the Y-axial threaded rod 23B. TheY-axial threaded rod 23B has its opposite ends rotatably connected tothe pair of X-axis nut elements 24A. The primary coil 11 is connected tothe Y-axis nut element 24B.

Further, in order to move the primary coil 11 in the direction of the Yaxis in a horizontal posture, the illustrated movement mechanism 13 hasa guide rod 26 disposed in parallel with the Y-axial threaded rod 23B.The guide rod 26 has its opposite ends connected to the pair of X-axisnut elements 24A, and moves together with the pair of X-axis nutelements 24A. The guide rod 26 extends through a guide portion 27connected to the primary coil 11 so as to enable the primary coil 11 tomove along the guide rod 26 in the direction of the Y axis. That is tosay, the primary coil 11 moves in the direction of Y axis in ahorizontal posture, via the Y-axis nut element 24B and guide portion 27which move along the Y-axial threaded rod 23B and the guide rod 26 whichare disposed in a mutually parallel relationship.

The movement mechanism 13 is so constructed and arranged that, when theX-axis servomotor 22A rotates the X-axial threaded rod 23A, the pair ofX-axis nut elements 24A move along the X-axial threaded rod 23A andallows the Y-axial threaded rod 23B and the guide rod 26 to move in thedirection of X axis. When the Y-axis servomotor 22B rotates the Y-axialthreaded rod 23B, the Y-axis net element 24B moves along the Y-axialthreaded rod 23B and allows the primary coil 11 to move in the directionof the Y axis. At this time, the guide portion 27 connected to theprimary coil 11 moves along the guide rod 26 and allows the primary coil11 to move in the direction of the Y axis in a horizontal posture.Therefore, the primary coil 11 can be moved in the directions of the Xaxis and the Y axis by controlling the rotation of the X-axis servomotor22A and Y-axis servomotor 22B by means of the position detectioncontroller 14. It should be noted that, in the battery charger cradle ofthe present invention, the movement mechanism is not limited to theabove-described mechanism. This is because every kind of mechanism isavailable as the movement mechanism that is moveable in the directionsof the X axis and the Y axis.

Further, in the battery charger cradle of the present invention, themovement mechanism is not limited to the mechanism that moves theprimary coil in the directions of the X axis and the Y axis. This isbecause the battery charger cradle of the present invention can have alinear guide wall provided on the top plate so as to be structured toplace the battery built-in device along the guide wall, allowing theprimary coil to move linearly along the guide wall. Although notillustrated, the battery charger cradle may have a movement mechanismthat allows the primary coil to move in a single direction, for example,in the direction of the X axis alone, thus moving the primary coillinearly along the guide wall.

The position detection controller 14 detects the position of the batterybuilt-in device 50 placed on the top plate 21. The position detectioncontroller 14 shown in FIG. 1 through FIG. 4 detects the position of theinduction coil 51 contained in the battery built-in device 50 and bringsthe primary coil 11 closer to the induction coil 51. Further, theposition detection controller 14 includes a first position detectioncontroller 14A for roughly detecting the position of the induction coil51 and a second position detection controller 14B for preciselydetecting the position of the induction coil 51. The position detectioncontroller 14 roughly detects the position of the induction coil 51 bymeans of the first position detection controller 14A and controls themovement mechanism 13 to make the position of the primary coil 11 closerto the induction coil 51; and subsequently, the position detectioncontroller 14 precisely detects the position of the induction coil 51and controls the movement mechanism 13 to make the position of theprimary coil 11 precisely close to the induction coil 51. The batterycharger cradle 10 quickly and more precisely allows the primary coil 11to be brought closer to the induction coil 51.

As shown in FIG. 5, the first position detection controller 14A includesa plurality of position detection coils 30 fixed to the inner surface ofthe top plate 21, a pulsed power source 31 for supplying a pulse signalto the position detection coils 30, a receiver circuit 32 for receivingthe echo signal outputted to the position detection coil 30 from theinduction coil 51 which is excited by the pulse signal supplied from thepulsed power source 31 to the position detection coil 30, and adiscrimination decision circuit 33 for judging the position of theprimary coil 11 on the basis of the echo signal received by the receivercircuit 32.

The position detection coil 30 is composed of multiple rows and columnsof coils, with the multiplicity of position detection coils 30 beingfixed at prescribed intervals to the inner surface of the top plate 21.The position detection coil 30 includes a plurality of X-axis detectioncoils 30A for detecting an X-axis position of the induction coil 51, anda plurality of Y-axis detection coils 30B for detecting a Y-axisposition of the induction coil 51. Each of the X-axis detection coils30A is of a loop elongated in the direction of the Y axis, the pluralityof X-axis detection coils 30A being fixed at prescribed intervals to aninner surface of the top plate 21. A distance (d) between the adjacentX-axis detection coils 30A is set to be smaller than an outer diameter(D) of the induction coil 51, with the distance (d) between the X-axisdetection coils 30A being set to be preferably 1 to ¼ times the outerdiameter (D) of the induction coil 51. When the distance (d) is madesmaller, the X-axis detection coil(s) 30A can precisely detect theX-axis position of the induction coil 51. Each of the Y-axis detectioncoils 30B is of a loop elongated in the direction of the X-axis, withthe multiplicity of Y-axis detection coils 30B being fixed at prescribedintervals to the inner surface of the top plate 21. Like in the case ofthe X-axis detection coil 30A, a distance (d) between the adjacentY-axis detection coils 30B is also set to be smaller than an outerdiameter (D) of the induction coil 51, with the distance (d) between theY-axis detection coils 30B being set to be preferably 1 to ¼ times theouter diameter (D) of the induction coil 51. When the distance (d) ismade smaller, the Y-axis detection coil(s) 30B can also precisely detectthe Y-axis position of the induction coil 51.

The pulsed power source 31 outputs a pulse signal to the positiondetection coil 30 at a prescribed timing. The position detection coil 30to which the pulse signal is inputted excites the approaching inductioncoil 51 by the pulse signal. The excited induction coil 51 outputs theecho signal to the position detection coil 30 by the energy of a flowingcurrent. Therefore, in the position detection coil 30 located near theinduction coil 51, as shown in FIG. 7, after the pulse signal has beeninputted, the echo signal from the induction coil 51 is induced with aprescribed delay time. The echo signal induced to the position detectioncoil 30 is outputted to the discrimination decision circuit 33 by meansof the receiver circuit 32. Therefore, the discrimination decisioncircuit 33, on the basis of the echo signal inputted from the receivercircuit 32, judges whether the induction coil 51 is brought closer tothe position detection coil 30. When the echo signal is induced to themultiplicity of the position detection coils 30, the discriminationdecision circuit 33 judges that the induction coil 51 is brought closestto the position detection coil 30 having the largest level of echosignal.

In the position detection controller 14 shown in FIG. 5, each of theposition detection coils 30 is connected to the receiver circuit 32 viaa switching circuit 34. In the position detection controller 14, sincethe connection is established with the plurality of position detectioncoils 30 by switching an input one after another, the echo signal fromthe plurality of position detection coils 30 can be detected by usingone single receiver circuit 32. However, the echo signal can also bedetected by connecting the receiver circuit to each of the positiondetection coils.

In the position detection controller 14 shown in FIG. 5, the connectionto the receiver circuit 32 is established by sequentially switching themultiplicity of position detection coils 30 at the switching circuit 34controlled by the discrimination decision circuit 33. The pulsed powersource 31 is connected to the output side of the switching circuit 34and outputs the pulse signal to the position detection coil 30. Thelevel of pulse signal outputted from the pulsed power source 31 to theposition detection coil 30 is very large when compared with the echosignal from the induction coil 51. The receiver circuit 32 is connectedat the input side to a limiting circuit 35 composed of a diode. Thelimiting circuit 35 limits the signal level of the pulse signal inputtedfrom the pulsed power source 31 to the receiver circuit 32 to beinputted to the receiver circuit 32. An echo signal with its smallersignal level is inputted to the receiver circuit 32 without beinglimited. The receiver circuit 32 amplifies and outputs both of the pulsesignal and the echo signal. The echo signal outputted from the receivercircuit 32 is a signal being delayed after the pulse signal at aprescribed timing, for example, by several μsec to several hundred μsec.Since a delay time of the echo signal after the pulse signal is aconstant one, a signal reaching at a prescribed delay time after thepulse signal is treated as an echo signal, and the level of the echosignal serves for judging whether the induction coil 51 is broughtcloser to the position detection coil 30.

The receiver circuit 32 is an amplifier for amplifying and outputtingthe echo signal inputted from the position detection coil 30. Thereceiver circuit 32 outputs the pulse signal and the echo signal. Thediscrimination decision circuit 33 judges whether the approach of theinduction coil 51 to the position of the detection coil 30 is set on thebasis of the pulse signal and the echo signal which are inputted fromthe receiver circuit 32. The discrimination decision circuit 33 isprovided with an A/D converter for converting the signal, inputted fromthe receiver circuit 32, to a digital signal. The digital signaloutputted from the A/D converter 36 is calculated to detect the echosignal. The discrimination decision circuit 33 detects the signalinputted at a delay time after the pulse signal as the echo signal, andalso judges from the level of the echo signal whether the induction coil51 is brought closer to the position detection coil 30.

The discrimination decision circuit 33 detects the X-axis position ofthe induction coil 51 by controlling the switching circuit 34 so as tosequentially connect the multiplicity of X-axis detection coils 30A tothe receiver circuit 32. Every time when each of the X-axis detectioncoils 30A is connected to the receiver circuit 32, the discriminationdecision circuit 33 outputs the pulse signal to the X-axis detectioncoil 30A connected to the discrimination decision circuit 33 and judgeswhether the induction coil 51 is brought closer to the X-axis detectioncoil 30A, based on whether or not the echo signal is detected at aprescribed delay time after the pulse signal. The discriminationdecision circuit 33 judges whether the induction coil 51 is broughtcloser to each of the X-axis detection coils 30A, by connecting all ofthe X-axis detection coils 30A to the receiver circuit 32. When theinduction coil 51 is brought closer to any of the X-axis detection coils30A, the echo signal is detected in a state that the X-axis detectioncoil 30A is connected to the receiver circuit 32. Therefore, thediscrimination decision circuit 33 can detect the X-axis position of theinduction coil 51 by means of the X-axis detection coil 30A which candetect the echo signal. In a state where the induction coil 51 isbrought closer across a plurality of X-axis detection coils 30A, theecho signal is detected from the plurality of X-axis detection coils30A,. In such state, the discrimination decision circuit 33 judges thatthe induction coil 51 is brought closest to the X-axis detection coil30A where the strongest echo signal, that is, the echo signal with alarge level is detected. The discrimination decision circuit 33 detectsthe Y-axis position of the induction coil 51 by similarly controllingthe Y-axis detection coil 30B.

The discrimination decision circuit 33 controls the movement mechanism13 on the basis of the detected X-axis and Y-axis directions, and movesthe primary coil 11 to a position closer to the induction coil 51. Thediscrimination decision circuit 33 controls the X-axis servomotor 22A ofthe movement mechanism 13 and moves the primary coil 11 to the X-axisposition of the induction coil 51. Further, the discrimination decisioncircuit 33 controls the Y-axis servomotor 22B of the movement mechanism13 and moves the primary coil 11 to the Y-axis position of the inductioncoil 51.

In the above-described manner, the first position detection controller14A moves the primary coil 11 to a position close to the induction coil51. In the battery charger cradle of the present invention, after thefirst position detection controller 14A has brought the primary coil 11closer to the induction coil 51, the battery 52 can be charged bycarrying the electric power from the primary coil 11 to the inductioncoil 51. In the battery charger cradle, however, after the position ofthe primary coil 11 is further controlled precisely to be brought closerto the induction coil 51, the battery 52 can be charged by carrying theelectric power. The primary coil 11 is brought more precisely closer tothe induction coil 51 by the second position detection controller 14B.

The second position detection controller 14B, using the AC power source12 as the self-excited oscillation circuit, precisely detects theposition of the primary coil 11 on the basis of the self-excitedoscillating frequency and controls the movement mechanism 13. The secondposition detection controller 14B controls the X-axis servomotor 22A andthe Y-axis servomotor 22B of the movement mechanism 13, moves theprimary coil 11 in the directions of the X-axis and the Y-axis, anddetects the oscillating frequency of the AC power source 12. FIG. 8shows the characteristics where the oscillating frequency of theself-excited oscillation circuit varies. This figure shows the variationin the oscillating frequency with respect to a relative displacementbetween the primary coil 11 and the induction coil 51. As shown in thisfigure, the oscillating frequency of the self-excited oscillationcircuit becomes the highest at the position where the primary coil 11 isbrought closest to the induction coil 51, and the oscillating frequencybecomes lower in accordance with the relative displacement. Therefore,the second position detection controller 14B controls the X-axisservomotor 22A of the movement mechanism, moves the primary coil 11 inthe direction of the X-axis, and stops the primary coil 11 at theposition where the oscillating frequency becomes the highest. Likewise,the Y-axis servomotor 22B is controlled to move the primary coil 11 inthe direction of the Y-axis, and the primary coil 11 is stopped at theposition where the oscillating frequency becomes the highest. In theabove-described manner, the second position detection controller 14B canmove the primary coil 11 to the position closest to the induction coil51.

In the above-described battery charger cradle, the first positiondetection controller 14A roughly detects the position of the inductioncoil 51, and subsequently the second position detection controller 14Bperforms a fine adjustment to bring the primary coil 11 even closer tothe induction coil 51. In a position detection controller 64 asdescribed below in conjunction with FIG. 9, the primary coil 11 can bebrought closest to the induction coil 51 without performing such a fineadjustment.

As shown in FIG. 9, the position detection controller 64 includes aplurality of position detection coils 30 fixed to the inner surface ofthe top plate, a pulsed power supply 31 for supplying a pulse signal tothe position detection coil 30, a receiver circuit 32 for receiving theecho signal outputted to the position detection coil 30 from theinduction coil 51 which is excited by the pulse signal supplied from thepulsed power source 31 to the position detection coil 30, and adiscrimination decision circuit 73 for judging the position of theprimary coil 11 on the basis of the echo signal received by the receivercircuit 32. Further, in the position detection controller 64, thediscrimination decision circuit 73 is provided with a memory circuit 77for storing a level of the echo signal induced to each of the positiondetection coils 30 with respect to the position of the induction coil51, that is, as shown in FIG. 7, for storing a level of the echo signalinduced after a prescribed lapse of time by exciting each of theposition detecting coils 30 by the pulse signal. The position detectioncontroller 64 detects the level of the echo signal induced to each ofthe position detection coils 30, and compares such level with the levelof the echo signal stored in the memory circuit 77 to detect theposition of the induction coil 51

The position detection controller 64 works out the position of theinduction coil 51 on the basis of the level of the echo signal inducedto each of the position detection coils 30, in the following manner. Theposition detecting coil 30 shown in FIG. 9 includes a plurality ofX-axis detection coils 30A for detecting the X-axis position of theinduction coil 51 and a plurality of Y-axis detection coils 30B fordetecting the Y-axis position of the induction coil 51, and theplurality of position detection coils 30 are fixed at prescribedintervals to the inner surface of the top plate 21. Each of the X-axisdetection coils 30A is of a loop elongated in the direction of the Yaxis, while each of the Y-axis detection coils 30B is of a loopelongated in the direction of the X axis. FIG. 10 shows the level of theecho signal induced to the X-axis position detection coil 30A in a statewhere the induction coil 51 is moved in the direction of the X axis,with a horizontal axis depicting the X-axis position of the inductioncoil 51 and a vertical axis depicting the level of the echo signalinduced to each of the X-axis position detecting coil 30A. The positiondetection controller 64 can work out the X-axis position of theinduction coil 51 by detecting the level of the echo signal induced toeach of the X-axis position detection coils 30A. As shown in the figure,when the induction coil 51 is moved in the direction of the X axis, thelevel of echo signal induced to each of the X-axis position detectioncoils 30A is varied. For example, when the center portion of theinduction coil 51 is located at the center portion of the first X-axisposition detection coil 30A, the level of the echo signal induced to thefirst X-axis position detection coil 30A becomes the strongest, asindicated by spot A in FIG. 10. Further, when the induction coil 51 isintermediate between the first X-axis position detection coil 30A andthe second X-axis position detection coil 30A, the echo signals inducedto the first X-axis position detection coil 30A and the second X-axisposition detection coil 30A are of the same level. That is to say, ineach of the X-axis position detection coils 30A, the level of the echosignal induced when the induction coil 51 is located the closest becomesthe strongest, and the level of the echo signal becomes smaller as theinduction coil 51 moves away. Therefore, on finding which one of theX-axis position detection coils 30A exhibits the highest level of echosignal, it can be judged that the induction coil 51 is the closest toeither one of the X-axis position detection coils 30A. Further, in thecase where the echo signal is induced to the two X-axis positiondetection coils 30A, on finding that the echo signal is induced to theX-axis position detection coil 30A located in either one of thedirections from the X-axis position detection coil 30A detecting thestrong echo signal, it can be judged that the induction coil 51 isdisplaced in either one of the directions from the X-axis positiondetection coil 30A exhibiting the strongest echo signal, and also therelative position between the two X-axis position detection coils 30Acan be judged from the level ratio of the echo signals. For example,when the level ratio of the echo signals is 1 between the two X-axisposition detection coils 30A, the induction coil 51 can be judged to bepositioned in the center of the two X-axis position detection coils 30A.

The discrimination decision circuit 73 stores, in the memory circuit 77,the level of echo signal induced to each of the X-axis positiondetection coils 30A with respect to the X-axis position of the inductioncoil 51. When the induction coil 51 is placed, the echo signal isinduced to either one of the X-axis position detection coils 30A.Therefore, the discrimination decision circuit 73 detects the placementof the induction coil 51 on the basis of the echo signal induced to theX-axis position detection coil 30A, that is, the placement of thebattery built-in device 50 on the battery charger cradle 10. Further,when the level of the echo signal induced to either one of the X-axisposition detection coils 30A is compared with the level stored in thememory circuit 77, the X-axis position of the induction coil 51 can bejudged. The discrimination decision circuit stores, in the memorycircuit, a function specifying the X-axis position of the induction coillearned from the level ratio of the echo signals induced to the adjacentX-axis position detection coils, and the position of the induction coilcan also be judged from the function. The function is worked out bydetecting the level ratio of the echo signals induced to the respectiveX-axis position detection coils. The discrimination decision circuit 73detects the level ratio of the echo signals induced to the two X-axisposition detection coils 30A, and based on the detected level ratio, theX-axis position of the induction coil 51 between the two X-axis positiondetection coils 30A can be calculated and detected using the function.

The above description shows the method in which the discriminationdecision circuit 73 detects the X-axis position of the induction coil 51on the basis of the echo signal induced to the X-axis position detectioncoil 30A, while the Y-axis position of the induction coil 51 can also bedetected on the basis of the echo signal induced to the Y-axis positiondetection coil 30B, like in the case of the X-axis position.

When the discrimination decision circuit 73 detects the X-axis andY-axis positions of the induction coil 51, the position signal from thediscrimination decision circuit 73 allows the position detectioncontroller 64 to move the primary coil 11 to the position of theinduction coil 51.

It should be noted that, when a waveform echo as described above isdetected, the discrimination decision circuit 73 in the battery chargercradle can recognize and discriminate that the induction coil 51 ismounted to the battery built-in device 50. When a waveform other thanthe waveform of the echo signal is detected and discriminated, thediscrimination decision circuit 73 judges that a matter (for example, aforeign metal) other than the induction coil 51 is mounted to thebattery built-in device 50, and can cut the power supply. Further, whenthe waveform of the echo signal is not detected and discriminated, theelectric power is not supplied because the induction coil 51 is notmounted to the battery built-in device 50.

In a state where the position detection controller 14, 64 controls themovement mechanism 13 to bring the primary coil 11 closer to theinduction coil 51, the battery charger cradle 10 allows the AC powersource 12 to supply the AC power to the primary coil 11. The AC power atthe primary coil 11 is (electrically) carried to the induction coil 51and is used for charging the battery 52. When a full charge state of thebattery 52 is detected, the charging operation is stopped at the batterybuilt-in device 50 and a signal of a full charge state is transmitted tothe battery charger cradle 10. The battery built-in device 50 outputsthe signal of a full charge state to the induction coil 51, transmitsthe signal of a full charge state from the induction coil 51 to theprimary coil 11, and can transmit information of the full charge stateto the battery charger cradle 10. The battery built-in device 50 outputsto the induction coil 51 an AC signal of a frequency different from thefrequency of the AC power source 12, and the battery charger cradle 10receives the AC signal at the primary coil 11 and can detect the fullcharge state. Further, it is also practicable that the battery built-indevice 50 outputs a carrier wave of a specific frequency to theinduction coil 51 in a signal modulated by the signal of the full chargestate, the battery charger cradle 10 receives the carrier wave of thespecific frequency, and the signal is demodulated to detect the signalof the full charge state. The battery built-in device can alsoradio-transmit the signal of the full charge state to the batterycharger cradle to transmit the information on the full charge state. Thebattery built-in device incorporates a transmitter for transmitting thesignal of the full charge state, and the battery charger cradleincorporates a receiver for receiving the signal of the full chargestate. The position detection controller 14 shown in FIG. 6 incorporatesa full charge state detection circuit 17 for detecting the full chargestate of the built-in battery 52. The full charge state detectioncircuit 17 detects the signal of the full charge state outputted fromthe battery built-in device 50 and detects the full charge state of thebattery 52.

The battery charger cradle 10 allowing a plurality of battery built-indevices 50 to be placed on the top plate sequentially switches and fullycharges the batteries 52 contained in the plurality of battery built-indevices. The battery charger cradle 10 initially detects the position ofthe induction coil 51 of any one of the battery built-in devices 50,brings the primary coil 11 closer to that induction coil 51, and fullycharges the battery 52 contained in that battery built-in device 50.When the battery 52 contained in the battery built-in device 50 is fullycharged and the full charge state detector circuit 17 receives thesignal of the full charge state, the position detection controller 14detects the position of the induction coil 51 contained in a secondbattery built-in device 50 which is placed at a different position ofthe previously-mentioned battery built-in device 50, controls themovement mechanism 13 and brings the primary coil 11 closer to theinduction coil 51 contained in the second battery built-in device 50. Inthis state, the electric power is carried to the battery 52 contained inthe second battery built-in device 50 to fully charge the battery 52.Further, when the battery 52 contained in the second battery built-indevice 50 is fully charged and the full charge state detection circuit17 receives a signal of the full charge state from the second batterybuilt-in device 50, the position detection controller 14 further detectsthe induction coil 51 contained in a third battery built-in device 50,controls the movement mechanism 13, brings the primary coil 11 closer tothe induction coil 51 contained in the third battery built-in device 50,and fully charges the battery 52 contained in the third battery built-indevice 50. In the above-described manner, when a plurality of batterybuilt-in devices 50 are placed on the top plate 21, the battery built-indevices 50 are switched from one after another to fully charge thebuilt-in batteries 52. The battery charger cradle 10 stores the positionof the battery built-in device having been fully charged, and does notcharge the battery 52 contained in the battery built-in device 50 havingbeen fully charged. When it is detected that the batteries 52 containedin all the battery built-in devices placed on the top plate 21 have beenfully charged, the battery charger cradle 10 stops the operation of theAC power source 12 and stops charging the battery 52. Here, in theabove-described embodiment, the charging operation is to be stopped whenthe battery 52 contained in the battery built-in device 50 has beenfully charged, but when the battery 52 reaches a prescribed capacity,the charging operation may also be stopped, with the prescribed capacitybeing regarded as a full charge state.

The second position detection controller 14B shown in FIG. 6 judges therelative position between the primary coil 11 and the induction coil 51in accordance with a variation in the oscillating frequency of theself-excited oscillation circuit, but the second position detectioncontroller performing a fine adjustment of the relative position betweenthe primary coil and the induction coil can detect the relative positionof the primary coil with respect to the induction coil on the basis ofeither the power consumption of the AC power source supplying thevoltage and the electric power to the primary coil or the electriccurrent induced to the induction coil. The second position detectioncontroller may be a separately excited oscillation circuit because theoscillating frequency does not have to be varied.

With reference to FIG. 11, the second position detection controller 14Cfor detecting a relative position of the primary coil 11 with respect tothe induction coil 51 on the basis of the voltage at the primary coil 11rectifies the AC voltage generated at the primary coil 11 to convert toa direct voltage, and incorporates a voltage detection circuit 83 fordetecting such voltage. The second position detection controller 14Cmoves the primary coil 11 and detects the voltage at the primary coil 11by means of the voltage detection circuit 83. FIG. 12 shows thecharacteristics in which the voltage at the primary coil 11 varies withrespect to a relative position between the primary coil 11 and theinduction coil 51. The figure shows the variation in the voltage at theprimary coil 11 with respect to the relative displacement between theprimary coil 11 and the induction coil 51. As shown in this figure, thevoltage at the primary coil 11 becomes the lowest at a position wherethe primary coil 11 is brought closest to the induction coil 51, and thevoltage becomes higher as the relative position is displaced. Therefore,the second position detection controller 14C controls an X-axisservomotor 22A of the movement mechanism 13, moves the primary coil 11in the direction of the X axis, and stops the primary coil 11 at aposition where the voltage becomes the lowest. Further, the Y-axisservomotor 22B is likewise controlled to move the primary coil 11 in thedirection of the Y axis, and stops the primary coil 11 at a positionwhere the voltage at the primary coil 11 becomes the lowest. In theabove-described manner, the second position detection controller 14C canmove the primary coil 11 to a position closest to the induction coil 51.

With reference again to FIG. 11, the second position detectioncontroller 14C detecting the relative position of the primary coil 11with respect to the induction coil 51 on the basis of the powerconsumption at the AC power source 82 supplying the electric power tothe primary coil 11 incorporates a power consumption detection circuit84 detecting the power consumption at the AC power source 82. The secondposition detection controller 14C moves the primary coil 11 and detectsthe power consumption at the AC power source 82 by means of the powerconsumption detection circuit 84. FIG. 13 shows the characteristics inwhich the power consumption at the AC power source 82 varies withrespect to the relative position between the primary coil 11 and theinduction coil 51. The figure shows the variation in the powerconsumption at the AC power source 82 with respect to a relativedisplacement between the primary coil 11 and the induction coil 51. Ascan be seen in the figure, the power consumption at the AC power sourcebecomes the smallest at a position where the primary coil 11 is broughtclosest to the induction coil 51, and the power consumption becomeslarger as the relative position is displaced. Therefore, the secondposition detection controller 14C controls the X-axis servomotor 22A ofthe movement mechanism 13, moves the primary coil 11 in the direction ofthe X axis, and stops the primary coil 11 at a position where the powerconsumption at the AC power source 82 becomes the smallest. Further,Y-axis servomotor 22B is likewise controlled to move the primary coil 11in the direction of the Y axis, and stops the primary coil 11 at aposition where the power consumption at the AC power source 82 becomesthe smallest. In the above-described manner, the second positiondetection controller 14C can move the primary coil 11 to a positionclosest to the induction coil 51.

With reference again to FIG. 11, the second position detectioncontroller 14C detecting the relative position of the primary coil 11with respect to the induction coil 51 on the basis of the currentflowing through the induction coil 51 incorporates a circuit fordetecting the electric current flowing through the induction coil 51.The second position detection controller 14 includes a transmittercircuit 95 for detecting, on the side of the battery built-in device 90,the current flowing through the induction coil 51 and forradio-transmitting a carrier wave modulated by such detected current,and a receiver circuit 85 for receiving, on the side of the batterycharger cradle 80, the signal transmitted from the transmitter circuit95, and demodulating the signal to detect the current flowing throughthe induction coil 51. The second position detection controller 14Cmoves the primary coil 11 and detects the current flowing through theinduction coil 51. FIG. 13 shows the characteristics in which thecurrent flowing through the induction coil 51 varies with respect to therelative position between the primary coil 11 and induction coil 51. Thefigure shows the variation of the induction coil 51 with respect to arelative displacement between the primary coil 11 and the induction coil51. As shown in the figure, the current flowing through the inductioncoil 51 becomes the largest at a position where the primary coil 11 isbrought closest to the induction coil 51, and the electric currentbecomes smaller in accordance with displacement of the relativeposition. Therefore, the second position detection controller 14Ccontrols the X-axis servomotor 22A of the movement mechanism 13, movesthe primary coil 11 in the direction of the X axis, and stops theprimary coil 11 at a position where the current flowing through theinduction coil 51 becomes the largest. The Y-axis servomotor 22B islikewise controlled to move the primary coil 11 in the direction of theY axis, and stops the primary coil 11 at a position where the electriccurrent flowing through the induction coil becomes the largest. In theabove-described manner, the second position detection controller 14C canmove the primary coil 11 to a position closest to the induction coil 51.

Although the above-described movement mechanism 13 moves the primarycoil 11 in the directions of the X axis and the Y axis to bring theprimary coil 11 to a position closest to the induction coil 51, thepresent invention is not limited to a structure where the movementmechanism moves the primary coil in the directions of the X axis and theY axis to bring the position of the primary coil to be the closest tothe induction coil, but the primary coil can also be moved in a varietyof directions to be brought closer to the induction coil.

It should be apparent to those of ordinary skill in the art that whilevarious preferred embodiments of the invention have been shown anddescribed, it is contemplated that the invention is not limited to theparticular embodiments disclosed, which are deemed to be merelyillustrative of the inventive concepts and should not be interpreted aslimiting the scope of the invention, and which are suitable for allmodifications and changes falling within the scope of the invention asdefined in the appended claims. The present application is based onApplications No. 2007-325,662 filed in Japan on Dec. 18, 2007, No.2008-64,860 filed in Japan on Mar. 13, 2008, and No. 2008-293,933 filedin Japan on Nov. 17, 2008, the contents of which are incorporated hereinby references.

1. A battery charger designed to be used with a battery built-in devicehaving an electromagnetically coupled induction coil incorporated in thebattery built-in device and a battery rechargeable with a power inducedby the induction coil, the battery charger comprising: a casing having atop plate; a primary coil connected to an AC power source for inducingelectromotive force to the induction coil, the primary coil beingseparated from the battery built-in device by the top plate; a movementmechanism for moving the primary coil along an inner surface of the topplate; and a position detection controller for detecting a position ofthe battery built-in device, the position detection controllercontrolling the movement mechanism to move the primary coil closer tothe induction coil contained in the battery built-in device, wherein thecasing houses the primary coil, the movement mechanism, and the positiondetection controller.
 2. The battery charger as recited in claim 1,wherein: the position detection controller comprises a plurality ofstationary position detection coils so that, when the battery built-indevice is positioned relatively close to a top surface of the top plateof the casing, the position detection controller detects the position ofthe battery built-in device with the stationary position detectioncoils, and the position detection controller controls the movementmechanism so that the movement mechanism moves the primary coil alongthe inner surface of the top plate to bring the primary coil closer tothe induction coil contained in the battery built-in device; and theinner surface of the top plate is opposite relative to the top surfaceof the top plate.
 3. The battery charger as recited in claim 1, whereinthe position detection controller comprises a first position detectioncontroller for roughly detecting a position of the induction coilcontained in the battery built-in device and a second position detectioncontroller for precisely detecting the position of the induction coil,such that after the primary coil has been moved closer to the inductioncoil by the first position detection controller, the primary coil isthen moved even closer to the induction coil by the second positiondetection controller.
 4. The battery charger as recited in claim 3,wherein the first position detection controller comprises a plurality ofposition detection coils disposed at a side of the inner surface of thetop plate, a pulsed power source for supplying a pulse signal to theposition detection coil, a receiver circuit for receiving an echo signaloutputted to a position detection coil from an induction coil which isexcited by the pulse signal supplied from the pulsed power source to theposition detection coil, and a discrimination decision circuit forjudging a position of the induction coil on the basis of the echo signalreceived by the receiver circuit.
 5. A combination comprising: a batterybuilt-in device having an electromagnetically coupled induction coil anda battery rechargeable with a power induced by the induction coil; and abattery charger for charging the battery built-in device, the batterycharger comprising: a primary coil connected to an AC power source forinducing electromotive force to the induction coil; a casing housing theprimary coil and having a top plate which is configured to permit thebattery built-in device to be positioned relatively close to at a topsurface side of the top plate; a movement mechanism for moving theprimary coil along an inner surface of the top plate, the inner surfacebeing opposite relative to the top surface of the top plate; and aposition detection controller for detecting a position of the batterybuilt-in device when positioned close to the top plate and controllingthe movement mechanism to move the primary coil closer to the inductioncoil contained in the battery built-in device, wherein, when the batterybuilt-in device is positioned relatively close to the top surface of thetop plate of the casing, the position detection controller detects theposition of the battery built-in device, the position detectioncontroller controls the movement mechanism so that the movementmechanism moves the primary coil along the inner surface of the topplate to move the primary coil closer to the induction coil contained inthe battery built-in device.
 6. A method for charging a battery built-indevice by using a battery charger, the method comprising: detecting aposition of the battery built-in device by a position detectioncontroller when the battery built-in device is positioned relativelyclose to a top plate of a casing of the battery charger, the positiondetection controller being incorporated in the casing, and the batterybuilt-in device incorporating an electromagnetically coupled inductioncoil and a battery that is rechargeable with a power induced by theinduction coil; moving a primary coil along an inner surface of the topplate by a movement mechanism incorporated in the casing, the movementmechanism being controlled by the position detection controller to bringthe primary coil closer to the induction coil of the battery built-indevice, and the primary coil being contained in the casing and connectedto an AC power source for inducing electromotive force to the inductioncoil; and charging the battery by the power induced from the primarycoil to the induction coil when the induction coil iselectromagnetically coupled to the primary coil.